Solar collector

ABSTRACT

The invention relates to a solar collector for focusing solar radiation onto a focal line, said solar collector comprising a carrier for a grooved, arched reflector. According to the invention, the carrier comprises a plurality of molded grooves which each have a parabolic lateral edge; the molded grooves are surrounded by an outer film; the reflector consists of an elastic reflector material; and the form of the reflector is impressed on the elastic reflector material, directly or by inserting a carrier, by means of the parabolic lateral edge.

The present invention relates to a solar collecting module characterizedby the terms in claim 1.

Solar collectors of the above type use a parabolic shaped reflectingsurface to collect and focus sunlight onto a focal line. The reflectingsurface is moved along its horizontal axis to follow the movement of thesun during the day.

These solar trough collectors have proved themselves over many years andare manufactured with different mirror support structures.

Modern solar collectors are up to 100 meters long and are approximately6 meters wide.

They are driven using one or more electric motors.

As is evident from the dimensions of these collectors and the fact thatthey stand exposed to the weather they are subject to high wind forces.These wind forces place high demands on the collecting modules inrelation to the stability of the mirror support structures.

These forces are especially high in relation to the twisting ortorsional rigidity of the structure. The reflecting and concentratingproperties of the collectors are adversely affected by even smalldeformation and this affects the efficiency of the installation.

In order to provide enough resistance to these torsional deformationforces reticular tube structures are used to support the parabolicshaped mirrors. This uncoupling of support structure and pre-formedreflectors results in an extremely complex overall structure.

An example is the solar collector DE-A-198 01 078 which uses such areticular tube structure to support the reflector surface. The supportstructure is connected to a carrier tube, which provides the torsionalrigidity. The reticular support, however, does not contribute to thetorsional strength, which means that these constructions are still proneto torsional deformation.

Another example is the parabolic trough concentrator DE-A-197 44 767that likewise uses a reticular support structure.

Diagonal tubes connected to the individual support arms provide thetorsional rigidity. This type of construction is suitable solely forshort collector modules as the torsional rigidity is not optimal.

DE-A-199 52 276 presents a parabolic trough collector in which swivelingsupport arms are arranged on a central axis. Here also the torsionalrigidity originates only from the central axis tube. The arms themselvesdo not contribute to the torsional strength.

WO-A-02 103 256 demonstrates a parabolic solar collector which has acentral tube onto which side arms are mounted. This type of reflector isindeed relatively resistant to bending but has almost no torsionalrigidity.

The present invention is based on the task of building a solarcollector, which provides torsional rigidity in a simple construction.

This task is resolved by a solar collector module having the features ofclaim 1.

In the present invention forming ribs are surrounded by an outer skinlayer. Together these form an enclosed box construction, which possessesvery high torsional strength. In addition, the form ribs are alsoparabolic shaped on their concave edge so that the reflector materialtakes on the parabolic trough shape when impressed upon the reflector.This means that the reflecting surface material need not be rigid.Pre-formed parabolic mirrors, which are relatively expensive, are notnecessary. Instead, the material can be pliable.

This pliable reflector material can, for example, be delivered on a rolland then cut to the required size on site. Transport costs are, in thisway, considerably reduced and the reflector surface material itself isalso considerably cheaper than pre-formed parabolic mirrors.

The present invention has the advantage of high torsion strength andthat, not only pre-formed parabolic mirrors, but also pliable reflectormaterial can be utilized because the parabolic trough shape is impressedon the outer skin in the concave area of the form ribs.

A further embodiment provides that the form ribs demonstrate a sickleshape. Because of this sickle shape the whole support structure with itsouter skin has, essentially the form of a supporting wing. This is, forexample, familiar in aircraft or ship construction and possesses highrigidity in regard to bending and torsion factors.

In order to give the form ribs the desired shape in a simple manner theyare manufactured using a folding or rippling process so that a concavelateral edge results that is essentially parabolic shaped. At the sametime the edge opposite the parabolic edge can be arched.

Onto this closed, torsion rigid support construction, formed by the formribs and the outer skin the pliable reflector material is applied sothat it adopts the parabolic shape.

Preferably a trapezoidal metal sheet is laid onto the outer skin, whichlies on the parabolic lateral edge. This sheet has grooves runninglengthways along the curved trough shaped collector onto which thereflector material is laid. This has the advantage that the supportingsurfaces of the reflector material, formed by the grooves in thetrapezoidal sheet, are free from obstructions, for example, screw orrivet heads and that the grooves form parallel running, strip surfaceswhich support the shape of the reflector material. Thereby, too,compensation for materials with different heat expansion coefficients,for example, glass reflector materials and metal outer skin or supportstructure is achieved.

The grooves of the trapezoidal metal sheet form channels that are apt tobe sealed at their lateral ends. These kind of closed channels have theadvantage that they can be evacuated so that, when the pliable reflectorsurface material is placed onto the support surfaces of the grooves witha layer of adhesive between, the channels of the grooves can beevacuated and the reflector material is held in place. This can becontinued until the adhesive layer has sufficiently hardened. By thismeans, special clamping systems can be spared. Another possible methodfor pressing the pliable reflector material in place is that, afterlaying the reflector in place, the trough is closed at the lateral endsand filled with water. Through the water pressure the reflector materialis pressed onto the grooves while the adhesive hardens.

In an embodiment, the trapezoidal metal sheet is fixed, together withthe outer skin, to the form ribs using, for example, screws or rivets.In this way, a separate riveting or screwing process is avoided becausethe outer skin lies between the form ribs and the grooves of thetrapezoidal sheet and is held in place by the fastening of thetrapezoidal sheet to the form ribs.

As already mentioned, it is advantageous to glue the reflector materialto the grooves of the trapezoidal sheet. In this way, small deformationsin the surface of the reflector material are avoided. Apart from this,different materials, as well as glass, can easily be fixed to thetrapezoidal sheet.

In this way, the reflector material used in the present invention can bea metal or synthetic foil or a thin glass layer with a thickness of, forexample, 1 mm. The foil material having a reflecting upper surface andthe glass a reflecting surface on one or both sides.

These thin materials have the special advantage that a second or morelayers can be added to them. In this way repair is considerablysimplified. Due to environmental effects the reflector surfaces becomegradually “blind” in that the reflecting properties are adverselyaffected. They must then be either exchanged or the mirror surfacerenewed. Whereas the present invention allows for new layers ofreflecting material to be added.

Along the focal line of the collector provision is made for a receivingtube, which is supported by support arms. These are attached to the formribs and/or the upper surface of the reflector (16).

This simple structure contributes to an inexpensive construction of thepresent invention.

Further advantages, characteristics and details of the present inventionare contained in the following description in which especially preferredembodiments are represented in detail with reference to the drawings.

The characteristics represented in the drawings as well as thosementioned in the description and/or the claims can relate individuallyor in any combination to the present invention.

The drawings show:

FIG. 1 A perspective representation of a reflector module.

FIG. 2 The support structure of a reflector module.

FIG. 3 Lateral view of a form rib in the direction of arrow 111 in FIG.2.

FIG. 4 A blank cutting for form ribs.

FIG. 5 a to 5 c Details of production steps in the manufacture of a formrib.

FIG. 6 An alternative drive for a reflector module installed on a levelbase.

FIG. 1 shows a reflector module (10), a plurality of which constitute asolar collector plant.

This reflector module (10) is fastened to a support structure (notshown) and is arranged so that the incident sun's rays strike theconcave area (12) and from there are reflected onto a receiving tube(14) (see FIG. 3). For this the concave area (12) is formed from aparabolic shaped reflector.

The reflector module (10), as schematically represented in FIG. 2,consists of a plurality of form ribs (18), which lay parallel to eachother. The form ribs (18) are clad on their concave edge (12) and theirconvex edge (20) with an outer skin (22) as represented in FIG. 1. Theouter skin (22) is fixed to the form ribs (18) by means of screws,rivets or some other means. In this manner the form ribs (18) and theouter skin (22) form an enclosed support structure.

In FIG. 3 rivets are schematically represented by means of which theform ribs (18) and the lower section (26) of the outer skin arefastened.

An upper section (28) of the outer skin (22) is laid onto the concaveedges (12) of the form ribs (18) and onto this upper section (28) of theouter skin (22) a trapezoidal metal sheet (30) is laid. The lowerbridges (32) of the trapezoidal sheet (30) together with the interposedupper section (28) of the outer skin (22) are then riveted to the formribs (18). The upper bridges (36) of the trapezoidal sheet (30) now formthe laying surface for a reflector material (38), which is pliable andrests on the upper bridges (36).

In this way the reflector material (38) adopts the characteristic shapeof the concave surface of the trapezoidal sheet (30). This shape is thedesired parabolic form, which allows the incident sun's rays to bedirected onto the receiving tube (14). The reflector material (38),which can consist of a reflecting metal or synthetic foil or a layer ofthin glass mirror having a thickness of, for example, 1 mm is then gluedto the upper bridges (36).

FIG. 3 shows, in addition, a support arm (40) apt to carry the receivingtube (14). These arms are fastened by rivets or some other means to thereflector (16) together with the upper bridges (36) of the trapezoidalsheet (30) and or with the underlying form ribs (18).

FIG. 4 shows a metal strip (ref. No 42) with a width of 1200 mm out ofwhich alternating blanks (44) are cut each blank being 6000 mm long.These blanks (44) or (46) as shown in FIG. 5 a are further processedwith a metal folding machine (not shown) in that they are bent to formthe concave area (12) contained in the lateral edge (48). This isachieved by rippling (50) or folding. The section thus formed still hasan essentially angular outer form that is chamfered in the nextproduction stage by pressing or folding. During this production stagethe lateral edge (48) is cut and or flanged so that, after laying theouter skin (22), the trapezoidal sheet (30) and the reflector material(38) onto the upper section (26), all have the desired parabolic shape.

In addition recesses (52) are introduced through which pipes for liquidsand electric power cables can run inside the reflector module (10). Therivets are fastened through the flanged edges.

Altogether it can be see that the present invention comprising aplurality of reflector modules (10) possesses the considerable advantagethat each reflector module (10) has the required torsion rigidity andthat pliable reflector material (38) can be used onto which theparabolic shape is impressed by the trapezoidal sheet (30) and the formribs (18). It is therefore not necessary to use expensive pre-formedrigid mirrors. Relatively inexpensive foil materials can be utilized orthin glass mirror, which are also less expensive.

The bonding bridges (54) connecting the upper bridges (36) and the lowerbridges (32) balance different heat expansion coefficients between thereflector material (38) and the outer skin (22) without problem. In thisway heat stress factors do not build up.

In an embodiment represented in FIG. 6 the reflector modules (10) lie ona level base and can be swiveled by means of a suitable drive. The lowersection (26) of the outer skin (22) is provided with a cogging, whichengages, with another cogging or a pair of cogwheels mounted on thebase. This type of fixed reflector module (1) is even more resistant tobuckling than hanging modules. They are also less exposed to the wind.

1-11. (canceled)
 12. A solar collector module to focus the sun's raysonto a focal line, the module comprising: a support structure, saidsupport structure having a plurality of form ribs, each of said formribs having parabolic lateral edges; an outer skin, said outer skinsurrounding said support structure such that said form ribs are clad insaid outer skin; and a trough-shaped, arched reflector, said reflectorhaving a pliable reflector material and a shape defined by saidparabolic lateral edges of said form ribs.
 13. The module of claim 12,wherein said reflector is disposed directly on said outer skin.
 14. Themodule of claim 12, further comprising a carrier disposed between saidouter skin and said reflector.
 15. The module of claim 12, wherein saidform ribs have a sickle shape.
 16. The module of claim 12, wherein saidparabolic lateral edges of said form ribs are established by folding orcorrugating said form ribs.
 17. The module of claim 12, wherein anopposing side of said parabolic lateral edges has a partially circularcontour.
 18. The module of claim 12, wherein said form ribs and saidouter skin constitute an enclosed rigid box structure.
 19. The module ofclaim 12, further comprising a trapezoidal metal sheet disposed betweensaid reflector material and said outer skin to seat on said paraboliclateral edges of said form ribs, said metal sheet having longitudinalgrooves running along said trough-shaped reflector, wherein saidreflector material seats on said metal sheet.
 20. The module of claim19, wherein said grooves form channels, structured to be sealed at endsthereof.
 21. The module of claim 19, wherein said trapezoidal metalsheet and said outer skin are attached to said form ribs.
 22. The moduleof claim 21, wherein said metal sheet and said outer skin are attachedto said form ribs using screws, rivets, or adhesive.
 23. The module ofclaim 19, wherein said reflector material is glued to said grooves ofsaid trapezoidal metal sheet.
 24. The module of claim 12, wherein saidreflector material comprises a metal, a plastic foil, or a thin glasslayer, wherein said foil has a reflective surface on its upper side andsaid glass has a reflective surface on one or both sides.
 25. The moduleof claim 24, wherein said foil or said glass layer has a thickness onthe order of 1 mm.
 26. The module of claim 12, further comprising meansfor a receiving tube disposed along the focal line and supported bysupport arms, wherein said support arms are connected to said form ribsand/or to an upper surface of said reflector.